The present invention relates to locknuts, and more particularly to locknuts including a locking coil.
Locknuts (also known as lock nuts, locking nuts, prevailing torque nuts, stiff nuts, and elastic stop nuts) are nuts that resist loosening under vibrations and torque.
One type of locknut includes a nut body and a locking coil within the nut body that acts as a locking element. In the installation or tightening direction, the nut body dilates the locking coil, which causes the coil to loosen its grip on the threaded member to permit relatively easy rotation. In the removal or loosening direction, the nut body contracts the locking coil, which causes the coil to tighten its grip on the threaded member to prevent unintended relative rotation (i.e. loosening). When the locknut is tightened against an object, a force balance exists between (a) the force of the face of the nut body against the object and (b) the force of the dilated locking coil against the interior perimeter of the nut body. The interior force is absorbed and managed by the inner diameter (ID) of the nut body.
In this type of locknut, both the nut body and the locking coil are fabricated of metal in order to withstand the described forces. While applications exist where a plastic nut body might be desired, a plastic nut body has not proven to be practical. This is because the force of the dilated metal locking coil on the plastic nut body over time will cause the nut body to experience creep (also known as cold flow), which is product deformation at ambient temperature under force over time. As the plastic creeps under load, the retention force balance will degrade, will fall out of specification, and eventually may decrease to such a state that the jointed retention will be lost completely. Consequently, plastic nut bodies are not a practical option for a locknut.